Wireless communication system

ABSTRACT

A communication system having at least one user worn receiver unit for receiving audio signals via a wireless audio link connected to a stimulating means for stimulating the user&#39;s hearing according to audio signals received via the audio link; and a plurality of user worn transmission units and a microphone arrangement for capturing audio signals from the respective user&#39;s voice, an audio signal transmission portion for establishing the wireless audio link to at least one receiver unit to transmit the captured audio signals to the at least one receiver unit, an assistive digital link transceiver portion for establishing a bidirectional assistive digital link to at least one of the other transmission units and/or to an external command unit, and a control unit for controlling signal transmission of the transmission unit according to data exchanged with the control unit of the at least one of the other transmission units and/or the external command unit.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a communication system comprising atleast one receiver unit to be worn by a user for receiving audio signalsvia a wireless audio link and a plurality of transmission units eachadapted to be worn by a user and comprising a microphone arrangement forcapturing audio signals from the respective user's voice, which can betransmitted to the receiver unit(s).

2. Description of Related Art

Usually in such systems, wherein the receiver unit usually is worn atear-level, the wireless audio link is an FM radio link. The benefit ofsuch systems is that sound captured by a remote microphone at thetransmission unit can be presented at a high sound pressure level to thehearing of the user wearing the receiver unit at his ear(s).

According to one typical application of such wireless audio systems, thestimulating means is a loudspeaker which is part of the receiver unit oris connected thereto. Such systems are particularly helpful for beingused in teaching e.g. (a) normal-hearing children suffering fromauditory processing disorders (APD), (b) children suffering a unilateralloss (one dead ear), or (c) children with a mild hearing loss, whereinthe teacher's voice is captured by the microphone of the transmissionunit, and the corresponding audio signals are transmitted to andreproduced by the receiver unit worn by the child, so that the teacher'svoice can be heard by the child at an enhanced level, in particular withrespect to the background noise level prevailing in the classroom. It iswell known that presentation of the teacher's voice at such enhancedlevel supports the child in listening to the teacher.

According to another typical application of wireless audio systems thereceiver unit is connected to or integrated into a hearing instrument,such as a hearing aid. The benefit of such systems is that themicrophone of the hearing instrument can be supplemented or replaced bythe remote microphone which produces audio signals which are transmittedwirelessly to the FM receiver and thus to the hearing instrument. FMsystems have been standard equipment for children with hearing loss(wearing hearing aids) and deaf children (implanted with a cochlearimplant) in educational settings for many years.

Hearing impaired adults are also increasingly using FM systems. Theytypically use a sophisticated transmitter which can (a) be pointed tothe audiosource of interest (in e.g. cocktail parties, (b) put on atable (e.g. in a restaurant or a business meeting), or (c) put aroundthe neck of a partner/speaker and receivers that are connected to orintegrated into the hearing aids. Some transmitters even have anintegrated Bluetooth module given the hearing impaired adult thepossibility to connect wirelessly with devices such as cell phones,laptops etc.

The merit of wireless audio systems lies in the fact that a microphoneplaced a few inches from the mouth of a person speaking receives speechat a much higher level than one placed several feet away. This increasein speech level corresponds to an increase in signal-to-noise ratio(SNR) due to the direct wireless connection to the listener'samplification system. The resulting improvements of signal level and SNRin the listener's ear are recognized as the primary benefits of FM radiosystems, as hearing-impaired individuals are at a significantdisadvantage when processing signals with a poor acoustical SNR.

International Patent Application Publication WO 02/23948 A1 relates to acommunication system comprising an FM receiver for a hearing aid,wherein audio signals may be transmitted from a plurality oftransmitters via an analog FM audio link and wherein in addition thetransmitters may transmit configuration parameters for adjusting the FMreceiver via a separate digital control channel which may use FSK(Frequency Shift Keying) modulation.

European Patent Application EP 1 638 367 A2 relates to a communicationsystem comprising an FM receiver unit for a hearing aid and atransmission unit comprising a microphone arrangement for capturingaudio signals from a user's voice. The audio signals are transmittedfrom the transmission unit to the receiver unit via an analog FM audiolink. In addition to the audio link a bidirectional digital link isprovided between the transmission unit and the receiver unit for pollingstatus information regarding the status of the receiver unit by thetransmission unit.

European Patent Application EP 1 657 958 A1 relates to a communicationsystem comprising a plurality of hearing devices which may communicateamong each other via a wireless link which may be analog or digital.

Usually analog audio FM receivers are highly optimized for low powerconsumption and small size. However, due to the analog nature of thiswireless link, multi-transmit structures are so far not possible withinsuch systems.

SUMMARY OF THE INVENTION

It is an object of the invention to provide for a communication systemwherein audio signals captured by the microphones of a plurality oftransmission units are transmitted to at least one receiver unit via awireless audio link, while the system should be particularly flexibleand easy to use.

The invention is beneficial in that, by combining a conventionalwireless audio link with an assistive digital link for controlling audiosignal transmission via the analog audio link, the flexibility and theuse comfort of conventional audio transmission systems can besignificantly enhanced.

In particular, if the audio link is an analog audio link, such as an FMor IR (infrared) link, the advantages of analog audio links such as thevery low power requirements, the lack of interference, the lack of audiodelay and the large implemented consumer base, can be combined with theadvantages of digital wireless links, such as the reliable dataexchange, the bidirectional communication and the possibility to createconfigurable networks. In particular, while the benefits of the analogaudio link can be essentially maintained, a relatively simple multi-usernetwork can be established, wherein the issue of which user's voice ispresently to be transmitted via the analog audio link to the receiverunit can be addressed in a manner which is very comfortable to theusers.

In some applications, the audio link may be a digital link rather thanan analog link. In this case the assistive digital link of the inventionmay serve to overcome range or bandwidth limitations of the digitalaudio link.

According to one embodiment, each transmission unit has an audiotransmission portion, with the assistive digital link (ADL) being usedto control which of the transmission units is presently allowed totransmit via the audio link. According to another feature of theinvention, only a part of the transmission units (usually only a singleone) is equipped with an audio transmission portion, while the audiosignals captured by the microphone arrangement of one of the othertransmission units is supplied via the assistive digital link to the (orone of the) audio transmission portion for being transmitted from therevia the audio link to the receiver unit(s).

These and further objects, features and advantages of the presentinvention will become apparent from the following description when takenin connection with the accompanying drawings which, for purposes ofillustration only, show several embodiments in accordance with thepresent invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic block diagram of an example of the architecture ofa communication system according to the invention ;

FIG. 2 is a schematic view of a first application example of the systemof FIG. 1;

FIG. 3 is a view like FIG. 2, with a second application example of thesystem of FIG. 1 being shown;

FIG. 4 is an example of a transmission unit to be used in the system ofFIG. 1;

FIG. 5 is a block diagram of one example of how the transmission unit ofFIG. 4 can be used in the system of FIG. 1;

FIG. 6 is a view like FIG. 5, with an alternative embodiment beingshown;

FIG. 7 is a view like FIG. 1, wherein an alternative example of thearchitecture of a communication system according to the invention isshown;

FIG. 8 is a schematic view of an application example of the system ofFIG. 7;

FIG. 9 is a block diagram of an example of one of the transmission unitsto be used in the system of FIG. 7; and

FIG. 10 is a block diagram of an example of another one of thetransmission units to be used in the system of FIG. 7.

DETAILED DESCRIPTION OF THE INVENTION

The communication system of FIG. 1 comprises at least one receiver unit10A and a plurality of transmission units 12A, 12B, 12C and 12D. Eachtransmission unit 12A, 12B, 12C and 12D comprises an analog transmissionportion 14, a microphone arrangement 16 and a digital transceiverportion 18. The microphone arrangement 16, which usually comprises twospaced apart microphones (see at 38A, 38B in FIG. 4) for enablingacoustic beam forming capability, is provided for capturing audiosignals from the respective user of the transmission unit 12A, 12B, 12Cand 12D, which audio signals may be transmitted by the analogtransmission portion 14 via an analog wireless audio link 20A, 20B, 20Cand 20D, respectively, to the receiver unit 10A.

The receiver 10A comprises or is connected to stimulating means 22A forstimulating the hearing of the user of the receiver unit 10A accordingto the audio signals received via the audio link 20A, 20B, 20C and 20D.The stimulating means 22A typically will be part of a hearinginstrument, in particular a hearing aid, and usually it will be aloudspeaker. The receiver unit 10A may be integrated into such hearinginstrument, or it may be connected to the hearing instrument, usuallyvia a so-called “audio shoe”. Usually the stimulating means 22A will beworn at least in part in the user's ear canal (for example, theloudspeaker may be worn in the ear canal, or a sound tube will beextending from the loudspeaker into the ear canal). The stimulatingmeans 22A may be part of a BTE (Behind The Ear)-, ITE (In The Ear)- orCIC- (Completely In the Channel) hearing instrument. In the latter case,also the receiver unit 10A will be worn at least in part in the user'sear canal; otherwise it will be worn at the user's ear.

It is to be understood that usually one of the receiver units 10A willbe provided for the right ear and one will be provided for the left ear.

The analog audio link 20A, 20B, 20C, 20D usually will be an FM link.

The communication system of FIG. 1 in addition to the receiver unit 10A,may comprise additional receiver units 10B, 10C, etc. which are to beused by other users. The analog audio links 20A, 20B, 20C, 20D will beused by these additional receiver units 10B, 10C in the same manner asby the receiver unit 10A.

The digital transceiver portions 18 serve to establish a bidirectionaldigital link 24A, 24B, 24C—assistive digital link (ADL)—to at least oneof the other digital transmitter portions 18 for exchanging data betweenthe transmission units 12A, 12B, 12C, 12D. This data may be used tocontrol transmission of audio signals via the analog audio link 20A,20B, 20C, 20D. Preferably audio signal transmission is controlled insuch a manner that at a time only one of the transmission units 12A,12B, 12C, 12D is allowed to transmit audio signals via the analog audiolink 20A, 20B, 20C, 20D.

The transmission units 12A, 12B, 12C, 12D may designed to be worn aroundthe respective user's neck or on the user's belt, etc.

Preferably, the digital link 24A, 24B, 24C, uses GFSK as the modulation,and it may use frequency hopping for achieving reliable datatransmission. Preferably, it may use the 2.45 GHz ISM band.Communication between the digital transmitter portions 18, which form anetwork, for example, may be organized according to a TDMA scheme.

In FIG. 4 an example of a block diagram of an example of thetransmission unit 12A (the transmission units 12B, 12C, 12D areidentical) is shown, according to which an antenna 26, a digitaltransceiver 27, a control unit 28, an audio signal processing unit 30,an analog transmitter 32, a power amplifier 34, an antenna 36 and themicrophone arrangement 16 comprising two spaced apart microphones 38A,38B are provided. The antenna 26 and the digital transceiver 27 form thedigital transceiver portion, whereas the analog transmitter 32, thepower amplifier 34 and the antenna 36 form the analog transmissionportion.

The audio signals captured by the microphones 38a, 38B are processed bythe audio signal processing unit 30, and then they are supplied to theanalog transmitter 32, from which the modulated audio signals aresupplied to the analog antenna 38, after amplification by the poweramplifier 34, in order to be transmitted via the analog audio link 20A.These elements correspond to the functionality of a conventional FMtransmission unit. However, in the embodiment of FIG. 4 the amplifier 34is controlled by the control unit 28, which exchanges data with theother transmission units 12B, 12C, 12D via the digital transceiverportion 27. Further, the control unit 28 communicates with the audiosignal processing unit 30. Usually the audio signal processing unit 30will include a voice activity detector in order to detect the timeperiods when the user of the transmission unit 12A is speaking.

When the voice activity detector has detected that the user is presentlyspeaking, a request for being allowed to transmit via the analog audiolink 20A, i.e. a request for the “right to transmit” is transmitted fromthe control unit 28 via the digital transceiver portion 18.

Preferably the communication protocol of the digital link 24A, 24B, 24Cis such that one of the transmission units, for example, thetransmission unit 12A, is the master, whereas the other transmissionunits, for example, 12B, 12C and 12D are the slaves. In this case themaster decides which one of the transmission units 12A, 12B, 12C, 12D isallowed to transmit via the analog audio link 20A, 20B, 20C and 20D,respectively. To this end, the master control unit 28 will transmitcorresponding commands via the digital link to the slave control units28. Unless the respective slave control unit 28 receives such an “FMenable” command, the control unit 28 will keep the power amplifier 34turned-off, thereby preventing analog audio signal transmission.

Since it may happen that two or more users are speaking at the sametime, it is necessary to define priority rules. One example of such apriority rule may be a “first come” principle, wherein once a certainone of the transmission units has been enabled to transmit via theanalog audio link, it will be allowed to continue until the respectiveuser has stopped speaking, i.e. until the respective voice activitydetector detects that the user has stopped speaking. During that time noother transmission unit will be allowed to transmit via the analog audiolink. Alternatively, or in addition, each of the transmission units maybe awarded a certain priority, with a transmission unit whose user isdetermined to presently speak is allowed to transmit via the analogaudio link only if none of the other transmission units having the sameor a higher priority has detected that the user of that transmissionunit is presently speaking. For transmission units having the samepriority, the “first come” principle will be applied.

According to FIG. 6, the communication protocol of the digital link maybe such that each slave control unit 28 communicates directly with themaster control unit 28 via the digital link.

An alternative scheme is shown in FIG. 5, according to which thecommunication protocol is such that the slave control units 28communicate with at least one of the other slave control units 28 viathe digital link in such a manner that each of those slave control units28 which do not directly communicate with the master control unit 28communicates with the master control unit via at least of the otherslave control units 28.

According to FIG. 2 the system of FIG. 1 is applied to a situation inwhich a user 40A of a hearing instrument comprising a receiver unit 10Acommunicates with other persons 42A, 42B, 42C, who are wearing atransmission unit 12A, 12B and 12C, respectively, in order to have theirvoices transmitted to the receiver unit 10A of the user 40A. Thetransmission units 12A, 12B, 12C are organized via the digital link 24A,24B in such a manner that at a time only one of the transmission units12A, 12B, 12C is allowed to transmit via the analog audio link. In theexample shown in FIG. 2 the person 42A is speaking, so that histransmission unit 12A detects his voice and is allowed to transmit theaudio signals captured by the microphones 38A, 38B of the transmissionunit 12A via the analog audio link 20A. Hence, in this example only theanalog audio link 20A from the transmission unit 12A is active, whereasthe analog audio links 20B and 20C from the transmission unit 12B, 12Care deactivated and are in a “waiting” status.

As already discussed above, preferably the request for the “right totransmit” via the analog audio link is generated upon detection of theuser's voice by a voice activity detector, which in a particularlyfavorable configuration requires the provision of two spaced apartmicrophones 38A, 38B at the transmission unit. In a simplified version,a single microphone input connected to an energy-based voice activitydetection algorithm could be used. However, rather than creating therequest for the “right to transmit” automatically, it is alsoconceivable that the person 42A, 42B, 42C who wants to speak generatesthe “right to transmit” request manually, for example, by pressing abutton at the transmission unit. Priority handling, i.e. if two personswish to speak at the same time, can be done in the same manner asdescribed for the voice activity detection, i.e. according topredetermined priorities plus “first come” for same priority.

According to a further alternative, the hearing instrument user 40A maybe provided with the option to select the person who he wants to hear.This can be done by providing him with a control box 44 comprisingcontrol elements 46, a digital transceiver 48 and an antenna 50. Thecontrol box 44 uses the same digital link (“ADL”) which is used for dataexchange between the transmission units 12A, 12B, 12C. By pressing therespective control element 46 the hearing instrument user 40A canactivate the desired one of the transmission units 12A, 12B, 12C. Tothis end the control box 44 transmits a corresponding command via thedigital link to the transmission units 12A, 12B, 12C, whereupon theselected one is allowed to transmit via the analog audio link. Forexample, the control elements 46 may comprise one button for each of thetransmission units.

In general, by using the communication system in the manner shown inFIG. 2 a “virtual microphone” is created which is passed around betweenthe persons 42A, 42B, 42C automatically and/or by interaction from thehearing instrument user 40A or the persons 42A, 42B, 42C. Suchapplication is useful in group communication situations, for example, ina business meeting, in a car, in a restaurant, or at home.

If the hearing instrument user 40A uses one receiver unit 10A at eachear, it would be possible to use different analog transmission channelson each ear. For example, the voices of the person 42A, 42B, 42C couldbe provided to one ear in the manner described above, whereas atelephone call, in particular a conference call, could be provided tothe other ear.

In the example of FIG. 2 all users of the transmission units 12A, 12B,12C are normal hearing persons. In FIG. 3 an example is shown in whichsome of the users of the transmission units are hearing impaired personswho wear a receiver unit.

A typical situation would be teaching in a specialized school forhearing impaired people. Traditionally, in such cases only the voice ofthe teacher 52A is broadcast via the analog audio link to the receiverunits worn by the students, whereas the answers from the students couldnot be heard by the other students via the receiver units.

FIG. 3 shows an example of how this deficiency can be overcome by usinga communication system according to the invention. Each of the students52B, 52C, 52D, 52E is provided with a transmission unit 12B, 12C, 12Dand 12E, respectively. The student 52E is normal hearing, whereas thestudents 52B, 52C and 52D are hearing impaired and therefore wear areceiver unit 10A, 10B and 10C, respectively. The audio signals capturedby that transmission unit which has received the “right to transmit”will be transmitted via the analog audio link to all receiver units. Thehandling of the “right to transmit” in generally may be similar to thatdiscussed with regard to the system shown in FIG. 2. However, usuallythe teacher 52A will be awarded the highest priority, i.e. if theteacher 52A speaks, his transmission unit 12A will always receive the“right to transmit” irrespective of whether another person is alreadyspeaking or wishes to speak.

As in the case of FIG. 2, a command unit 44 may be provided, which maybe used by the teacher 52A to select which student's voice is to betransmitted via the analog audio link.

As mentioned already with regard to FIG. 2, if the users wear tworeceiver units, two different analog audio channels my be realized, forexample, reception of the audio signals transmitted by the transmissionunits on one ear and audio signals from another audio source (telephoneetc.) at the other ear. It is also conceivable that the hearing impairedstudents receive the teacher's voice always on one ear and the student'sanswers in the other ear, if one of the students is active. If nostudent is active, the teacher's voice may be received on both ears.

In FIG. 8 a modification of the embodiment of FIG. 3 is shown, with therespective basic system architecture being schematically shown in FIG.7. According to this embodiment, only a few—usually only one—of thetransmission units comprises an analog transmission portion 14 and henceis adapted for audio signal transmission via the analog audio link 20Ato the receiver units 10A, 10B, 10C, whereas the other transmissionunits comprise only the digital transceiver portion 18 in order toparticipate in the digital link, but they do not participate in theanalog audio link 20A.

An example of a transmission unit 112A participating in the analog audiolink 20A is shown in FIG. 9. Similar to the example of the transmissionunit 12A shown in FIG. 4, the transmission unit 112A comprises anantenna 26, a digital transceiver 27, a control unit 28, two spacedapart microphones 38A, 38B, an audio signal processing unit 30, ananalog transmitter 32, a power amplifier and an antenna 36.

An example of the digital-only transmission units 112B, 112C, 112D isshown in FIG. 10, according to which an antenna 26, a digitaltransceiver 18, a control unit 28, an audio signal processing unit 30and two spaced apart microphones 38A, 38B are provided.

In the system of FIGS. 7 to 10 the digital link (“ADL”) is provided witha communication protocol which allows not only the exchange of controldata between the transmission units, which are necessary for organizingthe “right to transmit”, but in addition allows to digitally transmitaudio data corresponding to the audio signal captured by the microphonearrangement 16 of the digital-only transmission units, after having beenprocessed in the audio signal processing unit 30, via the digitaltransceiver 18 over the digital link to the other transmission units.Thereby the audio signals captured by each of the digital-onlytransmission units 112B, 112C, 112D can be transmitted via the digitallink to the analog-digital transmission unit 112A, In analogy to FIGS.1, 5 and 6, each digital-only transmission unit may communicate directlywith the analog-digital transmission unit 112A, or communication mayoccur indirectly via the closest one of the other digital-onlytransmission units.

The digital audio signals received by the digital transceiver portion 18of the analog-digital transmission unit 112A are supplied to the audiosignal processing unit 30 from where they can be transmitted in the samemanner as the audio signals captured by the microphones 38A, 38B of thetransmission unit 112A via the analog transmitter 32, the poweramplifier 34 and the antenna 36 over the analog audio link 20A to thereceiver units 10A, 10B, 10C. The control unit 28 of the transmissionunit 112A decides whether the audio signal is received via the digitallink from one of the digital-only transmission units is allowed to betransmitted via the analog audio link 20A or not. In this respect it isconceivable that transmission of the digital audio data via the digitallink is not controlled by the analog-digital transmission unit 112A, butthe analog-digital transmission unit 112A then will decide which of thereceived audio signal data is to be transmitted via the analog audiolink 20A. It is further possible to mix two or more audio streamstransmitted via digital links 24A, 24B, 24C in the analog-digitaltransmission unit 112A before transmission over the analog link 20A.Alternatively, the signals picked up by microphone arrangement 16 oftransmission unit 112A can be mixed with two or more audio streamstransmitted via digital links 24A, 24B, 24C in the analog-digitaltransmission unit 112A before transmission over the analog link 20A.According to an alternative model, the digital-only transmission unitsare allowed to transmit digital audio data to the analog-digitaltransmission unit 112A only if having been allowed by the analog-digitaltransmission unit 112A to do so.

The priority handling may be the same as discussed for the embodiment ofFIGS. 1 to 6. Preferably, the analog-digital transmission unit 112A willbe the master, whereas the digital-only transmission units 112B, 112C,112D will be the slaves.

FIG. 8 shows an example wherein the system architecture of FIG. 7 isapplied to the application shown in FIG. 3. In the embodiment of FIG. 8the teacher 52A is transmitting his voice in the same manner to thereceiver units 10A, 10B, 10C of the hearing impaired students 52B, 52C,52D as in the example of FIG. 3. However, the students' answers firstare transmitted in digital form via the digital link to the teacher'stransmission unit 112A, from where they are transmitted, if therespective student's transmission unit 112B has been awarded the “rightto transmit” by the control unit 28 of the teacher's transmission unit112A, is transmitted via the analog audio link 20A to the receiver units10A, 10B and 10C (in FIG. 8 the student 52B is speaking). Thereby theteacher's transmission unit 112A is used as a “hub”.

According to a modification of the embodiment of FIG. 3 and theembodiment of FIG. 8 a second teacher may be provided with a respectivetransmission unit so that he will also be able to transmit his voice viathe analog audio link. Priority handling between the transmission unitsof the two teachers may be the same as discussed, for example, withregard to FIG. 2, i.e. there may be a “first come” principle or one ofthe teachers may have higher priority.

As described in detail above, the digital link may be utilized forcontrolling the “right to transmit” via the analog audio link (FIGS. 1to 6) and in addition it may be used for transmitting audio signalsdigitally to a “analog audio transmission hub” (FIGS. 7 to 10). However,in addition a digital link also may be used for other purposes, such asbidirectional status reading of the various transmission units (forexample, battery power, etc.), software upgrade for the transmissionunits, remote control functionality, distribution of extracted audiodata and distance estimation between two transmission units, forexample, via RSSI functions (for example, the distance between a teacherand a student may be estimated), which may help, for example, withparing functions.

The transmission units worn by hearing impaired users may serve as aremote control for the respective receiver unit, for example via a 41kHz link. This is particularly beneficial for controlling the FMreceiver channel. Thereby the FM frequency management could besimplified. For example, if a certain FM channel is found to bedisturbed, a new one could be found and all FM receivers and FMtransmitters could be switched to this new channel. Communicationregarding the FM frequency between the FM transmitters would be achievedvia the digital link.

In some modified embodiments the analog audio link 20A, 20B, 20C, 20Dmay be replaced by a corresponding digital audio link.

While various embodiments in accordance with the present invention havebeen shown and described, it is understood that the invention is notlimited thereto, and is susceptible to numerous changes andmodifications as known to those skilled in the art. Therefore, thisinvention is not limited to the details shown and described herein, andincludes all such changes and modifications as encompassed by the scopeof the appended claims.

1. A communication system, comprising at least one receiver unit to beworn by a user, which is adapted for receiving audio signals via awireless audio link and which comprises or is connected to a stimulatingmeans for stimulating the user's hearing according to the audio signalsreceived via said audio link; a plurality of transmission units eachadapted to be worn by a user and comprising a microphone arrangement forcapturing audio signals from the respective user's voice, an audiosignal transmission portion for establishing said wireless audio link tosaid at least one receiver unit in order to transmit the captured audiosignals to said at least one receiver unit, an assistive digital linktransceiver portion for establishing a bidirectional assistive digitallink to at least one element of group consisting of the othertransmission units and/or to an external command unit, and a controlunit for controlling audio signal transmission of the transmission unitaccording to data exchanged with the control unit of said at least oneelement of the group consisting of the other transmission units and/orthe external command unit.
 2. The system of claim 1, wherein audiosignal transmission of said transmission units is controlled bycommunication of the control units the assistive digital link in such amanner that at a time only one of the transmission units is allowed totransmit audio signals via the audio link.
 3. The system of claimwherein the communication protocol of the assistive digital link is suchthat one of the control units a master and the other control units areslaves.
 4. The system of claim 3, wherein the communication protocol ofthe assistive digital link is such that each slave control unitcommunicates directly with the master control unit via the assistivedigital link.
 5. The system of claim 3, wherein the communicationprotocol of the assistive digital link is such that the slave controlunits communicate with at least one of the other slave control units viathe assistive digital link in such a manner that each of those slavecontrol units which do not directly communicate with the master controlunit communicate with the master control unit via at least one of theother slave control units.
 6. The system of claim 3, wherein each of thetransmission units comprises a voice activity detector (30) in order todetermine whether the user of the respective transmission unit ispresently speaking.
 7. The system of claim 6, wherein each transmissionunit which has detected that the respective user is presently speakingtransmits via the assistive digital link a request for being allowed totransmit via the audio link.
 8. The system of claim 7, wherein themaster control unit decides which one of the control units is allowed totransmit via the audio link and wherein the master control unittransmits via the assistive digital link corresponding commands to theslave control units.
 9. The system of claim 6, wherein each transmissionunit is awarded a certain priority and wherein a transmission unit whoseuser is determined to presently speak is allowed to transmit via theaudio link only if none of the other transmission units having the sameor a higher priority has detected that the user of that respectivetransmission unit is presently speaking.
 10. The system of claim 1,wherein at least one of the transmission units is manually operable bythe respective user for requesting the right to transmit audio signalsvia the audio link.
 11. The system of claim 1, wherein an externalcommand unit comprising an assistive digital link transceiver isprovided which is to be manually operated by the user(s) of the at leastone receiver unit or by the user of one of the transmission units inorder to determine which one of the transmission units is allowed totransmit via the audio link.
 12. A communication system, comprising atleast one receiver unit to be worn by a user, which is adapted forreceiving audio signals via a wireless audio link and which comprises oris connected to a stimulating means for stimulating the user's hearingaccording to the audio signals received via said audio link; and aplurality of transmission units each adapted to be worn by a user andcomprising a microphone arrangement for capturing audio signals from therespective user's voice, an assistive digital link transceiver portionfor establishing a bidirectional assistive digital link to at least oneof the transmission units for digitally transmitting audio signalscaptured by the microphone arrangement of the transmission unit and forexchanging control data with at least one element of the groupconsisting of the other transmission units and/or with an externalcommand unit; wherein at least one of the transmission units comprisesan audio signal transmission portion for establishing said audio link tosaid at least one receiver unit in order to selectively transmit audiosignals captured the microphone arrangement of that transmission unitand audio signals received from each one of the other transmission unitsto said at least one receiver unit, wherein selection of the audiosignals to be transmitted via the audio link occurs according to thedata exchanged between two elements of the group consisting of thetransmission units and the external command unit.
 13. The system ofclaim 12, wherein each transmission unit comprises a control unit forcontrolling assistive digital audio signal transmission of thattransmission unit according to control data exchanged with the controlunit of said at least one of the other transmission units.
 14. Thesystem of claim 13, wherein the communication protocol of the assistivedigital link is such that the control unit of the transmission unitcomprising the audio signal transmission portion is the a master and theother control units are slaves.
 15. The system of claim 14, wherein thecommunication protocol of the assistive digital link is such that eachslave control unit communicates directly with the master control unitvia the assistive digital link.
 16. The system of claim 14, wherein thecommunication protocol of the assistive digital link is such that theslave control units communicate with at least one of the other slavecontrol units via the assistive digital link in such a manner that eachthose slave control units which do not directly communicate with themaster control unit communicate with the master control units via atleast one of the other slave control units.
 17. The system of claim 16,wherein audio signal transmission via the audio link is controlled bycommunication of the control units via the assistive digital link insuch a manner that at a time only audio signals captured by themicrophone arrangement of one of the transmission units are transmittedvia the audio link.
 18. The system of claim 14, wherein each of thetransmission units comprises a voice activity detector in order todetermine whether the user of the respective transmission unit ispresently speaking.
 19. The system of claim 18, wherein eachtransmission unit which has detected that the respective user ispresently speaking transmits via the assistive digital data link arequest for being allowed to have the audio signals captured by thattransmission unit transmitted via the audio link.
 20. The system ofclaim 19, wherein the master control unit decides which one of thecontrol units is allowed to transmit via the audio link and transmitsvia the assistive digital link corresponding commands to the controlunits.
 21. The system of claim 18, wherein each transmission unit isawarded a certain priority and wherein a transmission unit whose user isdetermined to presently speak is allowed to transmit via the audio linkonly if none of the other transmission units having the same or a higherpriority has detected that the user of that respective transmission unitis presently speaking, with the transmission unit comprising the audiosignal transmission portion being awarded the highest priority.
 22. Thesystem of claim 1, wherein the audio link is an analog audio link. 23.The system of claim 22, wherein the audio link is a frequency modulationlink.
 24. The system of claim 1, wherein the assistive digital link usesGFSK-modulation.
 25. The system of claim 1, wherein the assistivedigital link uses frequency hopping.
 26. The system of claim 1, whereinthe assistive digital link uses a TDMA scheme.
 27. The system of claim1, wherein stimulating means is to be worn at least in part in theuser's ear canal
 28. The system of claim 1, wherein the receiver unit isto be worn at the user's ear or at least in part in the user's earcanal.
 29. The system of claim 1, wherein the transmission units areadapted to be worn around the respective user's neck.
 30. The system ofclaim 1, wherein the microphone arrangement comprises two or more spacedapart microphones.
 31. A use of a system of claim 1, wherein the systemcomprises a plurality of receiver units and wherein at least one of theusers uses one of the transmission units and one of the receiver units.32. The use of claim 31, wherein the digital link is used for at leastone of: reading of information regarding the status of the transmissionunits; upgrade of software of the transmission units; estimation of thedistance between two of the transmission units; distribution ofextracted audio data to the transmission units; and remotely controllingthe transmission units.
 33. A method of operating a communication systemcomprising at least one receiver unit worn by a user and a plurality oftransmission units each worn by a user and comprising a microphonearrangement an audio signal transmission portion an assistive digitallink transceiver portion and a control unit, said method comprising:establishing a bidirectional assistive digital link from eachtransmission unit to at least one of the other transmission units and/orto an external command unit; capturing audio signals from the respectiveuser's voice at at least one of the transmission units, establishing awireless audio link to said at least one receiver unit in order totransmit the captured audio signals to said at least one receiver unit,stimulating the hearing of the user(s) of the at least one receiver unitaccording to the audio signals received by the at least one receiverunit via said audio link, wherein audio signal transmission of eachtransmission unit is controlled according to data exchanged with thecontrol unit of at least one of the other transmission units and/or theexternal command unit via the assistive digital link.
 34. A method ofoperating a communication system comprising at least one receiver unitworn by a user and a plurality of transmission units each worn by a userand comprising a microphone arrangement and an assistive digital linktransceiver portion, wherein at least one of the transmission unitscomprises an audio signal transmission portion; the method comprising:capturing audio signals from the respective user's voice at at least oneof the transmission units, establishing a bidirectional assistivedigital link from each transmission unit to at least one of the othertransmission units for digitally transmitting audio signals captured bythe microphone arrangement of the transmission unit and for exchangingcontrol data with the at least one of the other transmission unit and/orwith an external command unit; establishing a wireless audio link fromsaid at least one least one transmission unit comprising the audiosignal transmission portion to said at least one receiver unit in orderto selectively transmit audio signals captured the microphonearrangement of that transmission unit and/or audio signals received viathe assistive digital link from at least one of the other transmissionunits to said at least one receiver unit, stimulating the hearing of theuser(s) of the at least one receiver unit according to the audio signalsreceived by the at least one receiver unit via the audio link, whereinselection of the audio signals to be transmitted via the audio linkoccurs according to the data exchanged between the transmission unitsand/or the external command unit.